Advance in manufacture of TFT technology consequently brings improvement to an LCD system such that the latter can be constructed in compact size with low power consumption and lower radiation. The TFT technology is employed in manufacture of personal computers, personal digital assistances (PDA), digital watches, notebook computers, digital cameras, mobile phones, and many other consumer electronics. The manufacturers worldwide have devoted themselves to further research and thus improve the materials, processes and equipments. The qualities of the LCD system are accordingly and largely promoted while the cost goes down day-by-day, which, in turn causes a wide use of the LCD system.
In order to enhance the response speed of the screen and to widen the viewable angle of the screen, researches are conducted relating to the characteristics of the material for constructing the liquid crystal layer. Presently, three types are proposed, namely, (1) Vertical Alignment mode; (2) Lowering the viscosity ratio within the liquid crystal layer in order to assist in alteration of the initial alignment of the liquid crystal molecules to a predetermined displayable alignment; and (3) OCB (optically compensated bend) mode.
In the OCB mode LCD system, the molecules near the upper and lower glass substrates are deployed in parallel directions while the liquid crystal molecules therebetween in the liquid crystal layer are not twisted but are operated in the bent alignment state with respect to a vertical plane. Such type of bent alignment can result in fast switching retardation of light. The residual phase difference during the dark state operation can be compensated by employment of a external retardation film so as to overcome the restricted viewing angle caused due to the parallel alignment of the liquid crystal molecules on the boundaries, thereby providing a wide viewable angle. In addition, the liquid crystal molecules in the OCB mode requires a fast response time of 1-10 ms to switch between dark and bright state operation when compared to the liquid crystal molecules of the TN (twisted nematic) mode which requires a response time of about 50 ms.
Note that, though the OCB mode LCD system has the aforesaid advantage, there still exist some disadvantages, such as it requires a longer warming-up time in order to perform the transition of the liquid crystal molecules in the liquid crystal layer from the splay alignment into the bend alignment. In the presently available OCB mode of LCD system, a high voltage is generally applied onto two opposite ends of the liquid crystal layer in order to quicken the transition of the liquid crystal molecules of the liquid crystal layer from the splay alignment into the bend alignment.
Referring to FIG. 1, a circuit diagram of a pixel unit of the prior art LCD system is shown, in which a TFT (thin film transistor) serves as a switch. The TFT 10 includes a gate coupled to a gate driver 13 via a scanning line 12, a source coupled to a source driver 15 via a data line 14, and a drain coupled to an auxiliary capacitor (Cst) and a pixel electrode 16. A common electrode 17 is disposed oppositely to the pixel electrode 16. A liquid crystal layer 18 is disposed between the pixel electrode 16 and the common electrode 17. When the gate driver 13 inputs a scanning signal (Vg) so as to switch on the TFT 10, the data signal (Vdata) from the source driver 15 can be transfer to the pixel electrode 16 via the drain such that a voltage difference between the pixel electrode 16 and common electrode 17 causes an image display on the screen.
According to the conventional LCD system, the construction design of the source driver 15 can be altered to increase the voltage level (such as from 5 to 15 volts) in order to apply a high voltage level on the pixel electrode 16 to perform the transition of the liquid crystal molecules in the liquid crystal layer 18. Alternatively, the circuit connected with the common electrode 17 can be altered in such a manner to lower the voltage level (such as from 6 to −16 volts) to result in a greater voltage difference between the pixel electrode 16 and common electrode 17. The aforesaid alteration of the source driver 15 or the circuit connected with the common electrode 17 may bring inconvenience to the manufacturers in addition to an extra production cost.